1. Field of the Invention
The invention relates to an image forming apparatus such as a laser beam printer or a copying machine for forming an image on a recording material by the use of an electrophotographic printing method or an electrostatic recording method. More particularly, this invention relates to a developer layer thickness regulating member for use in a developing apparatus using a mono-component developer, and a developing apparatus, a cartridge and an image forming apparatus provided with the same.
2. Description of the Related Art
An electrophotographic image forming apparatus such as, for example, a copying machine or a laser beam printer applies light corresponding to image data to an electrophotographic photosensitive member (photosensitive member) to thereby form an electrostatic image (latent image). Then, the toner of a developer which is a recording agent is supplied from a developing apparatus to the electrostatic image to thereby visualize the electrostatic image as a toner image. This toner image is transferred from the photosensitive member to a recording material such as recording paper by a transferring device. This toner image is fixed on the recording material by a fixing device, whereby a recorded image is formed.
There have been proposed various developing apparatuses using a dry type mono-component developing method. The following may be taken as an example. A magnetic mono-component developer (magnetic toner) is carried on a developing sleeve as a developer carrying member, and a uniform toner layer is formed by a developer regulating member for regulating the layer thickness of the developer. This developing sleeve is brought into proximity to or contact with the photosensitive member. Then, for example, a developing bias voltage comprising an AC component and a DC component is applied to the developing sleeve to thereby generate a potential difference between the electrostatic image on the photosensitive member and the developing sleeve. Thereby, the toner is moved to the electrostatic image to thereby effect development.
Further describing, such a developing apparatus has a cylindrical developing sleeve rotatably provided in the opening portion of a developer container containing a magnetic toner therein. In this developing sleeve, there is provided magnetic field generating means (magnetic roller) provided with a plurality of magnetic poles and fixedly disposed. The magnetic toner is attracted onto the developing sleeve by a magnetic field generated by this magnetic field generating means, whereby the toner is carried on the developing sleeve and is conveyed. Also, in such a developing apparatus, a toner layer is formed on the developing sleeve by the developer regulating member abutting against the developing sleeve. As the developer regulating member, use is generally made of a blade-shaped member (hereinafter referred to as the “developing blade”) formed of an elastic material.
On the other hand, there is the following method as another method using the dry type mono-component developing method. A nonmagnetic mono-component developer (nonmagnetic toner) is applied onto a developing roller as a developer carrying member by a supplying roller as a developer supplying member. The toner is carried on the developing roller and is conveyed and also, a toner layer is formed on the developing roller by the developer regulating member. This developing roller is brought into proximity to or contact with the photosensitive member to thereby effect development. At this time, a developing bias voltage similar to that mentioned above can be applied to the developing roller.
Further describing, such a developing apparatus has a developing roller rotatably provided in the opening portion of a developer container containing a nonmagnetic toner therein. Also, it has a supplying roller formed of a foam or the like and rotated while being in contact with the developing roller. The developing roller and the supplying roller are rotated in counter directions. The supplying roller has also the action of applying the nonmagnetic toner onto the developing roller and at the same time, scraping off the toner residual on the developing roller (hereinafter referred to as the “developing residual toner”) after having passed a developing position.
In recent years, improvements in the resolution, sharpness, etc. of an image have been required and therefore, the toner used in the developing apparatus has been advanced in the tendency toward a spherical shape and a smaller particle diameter. Particularly, the toner made spherical has been used because it becomes higher in the charging amount Q [μC/g] per weight, and is effective for an improvement in the reproduction of a dot image and thin-line image, and is improved in transferability.
However, the use of the toner made spherical may pose the following problem.
A toner having a high degree of sphericity has the tendency that the toner conveyance amount M [g/m2] passing the developing blade on the developing sleeve and conveyed to a developing area increases. This tendency appears during low coverage rate print (the output of an image low in image ratio) or after an idle rotating operation.
Also, there is a case where due to an excessive increase in the toner conveyance amount, variation in the distribution of the charging amount of the toner occurs to thereby cause unevenness of a toner coat on the developing sleeve, and uneven image density occurs.
Also, due to the increase in the toner conveyance amount, charge imparting to the toner is liable to become insufficient between the developing sleeve and the developing blade. There is also a case where the insufficient charged toner is conveyed to the developing area, whereby there occurs a so-called fogged image in which the toner adheres to other portion (non-image portion) than the electrostatic latent image on the photosensitive member.
It has been found that this tendency is particularly remarkable in a developing apparatus using a magnetic mono-component developer (magnetic toner). This is due largely to the fact that the toner is carried by the magnetic force of a magnet in the developing sleeve and therefore, there is not the action of scraping off the developing residual toner by the supplying roller as in a developing apparatus using a nonmagnetic mono-component developer (nonmagnetic toner).
That is, it is considered to be because the developing residual toner is not scraped off from the developing sleeve, but coats the developing sleeve together with a newly supplied toner and therefore there is a case where the toner coat becomes unstable.
As means for suppressing such an increase in. the toner conveyance amount M [g/m2] as described above, heretofore chiefly the following techniques (α) to (γ) have been combined together, whereby control has been effected.
(α) The surface roughness [μm] of the developing sleeve is made small.
(β) The abutting pressure P [g/cm] of the developing blade against the developing sleeve is heightened.
(γ) The distance (hereinafter referred to as the “NE length”) [mm] from the abutting position of the developing blade against the developing sleeve to the free end of the developing blade is shortened.
That is, the techniques (α) to (γ) are methods of mechanically regulating a toner conveying force and have a limit due to variation in manufacturing parts and variation in installation of parts. Also, an increase in the abutting pressure P [g/cm] increases mechanical stress given to the toner and promotes the deterioration of the toner, thus sometimes resulting in a reduction in image density. Also, when the surface roughness of the developing sleeve is set low, durability is reduced, and this becomes disadvantageous to the higher speed and longer life of the image forming apparatus.
There have been disclosed various techniques regarding a toner layer forming method by a developer regulating member.
There is a technique of prescribing the surface roughness Ra [μm] of a soft elastic member which is a developer layer forming member and the radius of curvature of a recess to thereby suppress the fluctuation of the toner conveyance amount for a long period of use (see Japanese Patent Application Laid-Open No. S62-242975).
Also, there is a technique of making the surface roughness of an elastic regulating member as a developer regulating member greater toward an upstream side relative to a downstream side with respect to the rotation direction of a developer carrying member to thereby give conveyance resistance to the toner and achieve the compatibility of stable layer thickness regulation and the uniform chargeability of the toner (see Japanese Patent Application Laid-Open No. H04-55872).
Also, there is a technique of designating the roughness of a layer forming member as a developer regulating member on the side thereof downstream of a position at which it abuts against a developer carrying member so as to be smaller than the roughness on the upstream side thereof, and/or forming a level difference shape on the side upstream of the abutting position (see Japanese Patent Application Laid-Open No. 2001-117356 and Japanese Patent Application Laid-Open No. 2001-117357). In these methods, the range prescription by the surface roughness Ra [μm] and/or the level difference height [mm] of the layer forming member is done.
Also, there is a technique of prescribing the surface roughness Rz of a thin layer forming blade as a developer regulating member to thereby increase the charging amount to a nonmagnetic mono-component developer (nonmagnetic toner) and achieve the prevention of a fogged image (see Japanese Patent Application Laid-Open No. H05-188748).
Also, there is a technique of prescribing the surface roughness Rz of a toner regulating member as a developer regulating member to thereby achieve the uniformization of the thin layer/an increase in the charging amount of a magnetic mono-component developer (magnetic toner), and achieve the higher quality of an image in the initial state of use (see Japanese Patent Application Laid-Open No. 2004-117919).
Also, there is a technique of providing streak-shaped unevenness at a pitch substantially parallel to a longitudinal direction on the surface of an elastic blade member as a developer regulating member and prescribing Rz to thereby achieve the maintenance of a stable toner charging amount for a long period of use (see Japanese Patent Application Laid-Open No. 2000-330376).
Also, there is a technique of prescribing the surface roughness Rz of a toner layer regulating member as a developer regulating member relative to the mean particle diameter of a toner to thereby utilize the clogging of toner particles on the rough surface of the toner layer regulating member (see Japanese Patent Application Laid-Open No. H09-080904). In this method, as described above, the toner particles are clogged to thereby enhance the degree of smoothness of the contact surface with a developing roller, and achieve the uniformization of the thin layer of the toner for a long period of use.
Also, there is a technique of prescribing the surface roughness Ra, Rz and Rmax of a developer regulating member to thereby achieve the uniformization of the thin layer of a toner on an elastic developing roller and the prevention of a faulty image after the elastic developing roller has been left unused for a long period of time (see Japanese Patent Application Laid-Open No. 2004-12542).
On the other hand, there is a proposition to contrive the formation of the uniform thin layer of a toner by controlling the coefficient of friction on the surface of a developer regulating member, instead of the surface shape (roughness) thereof as described above. That is, there is a technique of prescribing the magnitude relationships among the coefficients of friction of toners, the coefficients of friction of a layer thickness regulating member and the toner, and the coefficients of friction of a developing roller and the toner to thereby cause the toner layer to produce a shearing force, and achieve the formation of a thin layer of toner by a mechanical force (see Japanese Patent Publication No. H06-052448 and Japanese Patent Application Laid-Open No. 2000-227713).
Also, there is a technique of providing a charge uniformizing member discretely from a developer regulating member, and prescribing the magnitude relationship between the coefficients of kinetic friction thereof to thereby achieve the compatibility of the uniformized thin layer/uniform chargeability of a nonmagnetic mono-component toner (see Japanese Application Laid-Open No. 2000-275964).
Further, there is also a technique of providing a plurality of abutting members for a developer carrying member, and prescribing the magnitude relationship among the coefficients of friction thereof to thereby achieve the compatibility of the uniformized thin layer/uniform chargeability of a toner (see Japanese Patent Application Laid-Open No. 2002-023491).
However, it has been found that only by simply paying attention to Ra, Rz and Rmax regarding the surface roughness of the developer layer thickness regulating member as described above, it is difficult to achieve the compatibility of the stabilization of a developer layer thickness regulating force and the prevention of the occurrence of a streaked image.
Also, it has been found that only by prescribing the coefficient of surface friction of the developer layer thickness regulating member, it is difficult to achieve the compatibility of the stabilization of a toner regulating force and the prevention of the occurrence of a streaked image.